A communication system is a facility which facilitates communication between two or more entities such as communication devices, network entities and other nodes. A communication system may be provided by one or more interconnect networks. It should be appreciated that although a communication system typically comprises at least one communication network, for example a fixed line network, a satellite system, a wireless system or a mobile network, in its simplest form a communication system is provided by two entities communicating which each other. The communication may comprise, for example, communication of data for carrying communications such as voice, electronic mail (email), text messages, multimedia and so on. The user may communicate by means of an appropriate communication device such as user equipment.
An appropriate access system allows the communication device to access the communication system. An access to the communication system may be provided by means of a fixed line or wireless communication interface, or a combination of these. Examples of wireless access systems include cellular access networks, various wireless local area networks (WLANs), wireless personal area networks (WPANs), satellite based communication systems and various combinations of these.
A communications system typically operates in accordance with the standard and/or certain specifications and protocols which set out what the various elements of the system are permitted to do and how that should be achieved. For example, it is typically defined if the user, or more precisely user equipment is provided with a circuit switched bearer or a packet switched bearer or both. Also, the manner in which communication and various aspects thereof should be implemented between the user equipment and the various elements of the communication system and their function and responsibilities are typically defined by a predefined communication protocol.
Reference is made to the following document: IST-2003-507581 WINNER D6.1: WINNER Spectrum Aspects: Methods for Efficient Sharing, Flexible Spectrum Use and Coexistence. This document provides a background to the general concept of flexible spectrum use FSU and spectrum sharing SS in IMT (international mobile telecommunications)-A (advanced) systems.
FSU relates to flexible spectrum use. This refers to the concept of spatially and/or temporarily varying use of the radio spectrum. In other words, in a environment comprising more than one system, there is not an exclusive harmonised spectrum assignment.
Spectrum sharing refers to the situation where different systems or sub-systems utilise the same part of the spectrum in a coordinated or uncoordinated manner. A special case is sharing based on flexible spectrum use.
IMT-Advanced system refers to radio access systems beyond the IMT-2000 system. A global unified wireless architecture is proposed which visualises a hierarchy of interconnected access systems. This system envisages new radio interfaces with mobile class targeting for 100 Mbps and nomadic or local area class targeting for 1 GBPs. This may include operation on new spectrum or frequency bands which may or may not be licensed.
In the International Telecommunication Organization ITU there is under preparation spectrum allocation proposals for IMT-Advanced systems. In that context one proposal has been that the spectrum slots allocated to fixed satellite service (FSS) usage would be allowed a secondary usage for terrestrial wireless systems if the interference levels to a primary satellite system is kept in certain limits. The secondary wireless systems could be a cellular system or wireless local area network.
The interference to a primary satellite system may be severe in the vicinity of an earth station and for that reason it has been proposed that there will be an exclusion zone around an earth station where the secondary usage by a terrestrial system is not permitted or the power levels should be relatively low.
However, there is a problem in that with wireless systems it is difficult to define the exact coverage of a communication area, especially if user equipment is moving. This is means that it may be difficult to define which frequency slots are allowed in which areas and when to permit spectrum sharing.
One proposal is to use a beacon signal in those frequency slots which are allowed for spectrum sharing between a satellite and terrestrial system. In this scheme, devices of the terrestrial system should monitor that beacon. In this proposal, it is unclear as to the responsibility for the transmission of the beacon signal.
Another proposal is to calculate the contributions of different cells to the interference at an earth station. The transmit powers are set a maximum in the individual cells so that the interference remains below an acceptable interference threshold at the earth station.
Yet another proposal is to combine a positioning system with a mapping of the geographical area with allowed frequency slots. In this proposal, earth station locations should be known for the mapping and that is not always possible, especially in the case of temporary earth stations, e.g., moving earth stations provided in news vans such as CNN vans.
It is an aim of embodiments of the present invention to address one or more of the problems set out above.